The present invention relates to optical signal transmission systems or the like and more particularly to a mixer-based time domain reflectometer and method for detecting any reflections, anomalies or defects in a fiber optic transmission line or other optical medium.
Transmission lines are commonly employed to communicate signals between various portions of an electronic system. For example, coaxial transmission lines, waveguides, and even parallel arrangements of metallic conductors are typically employed as transmission lines in such systems. Increasingly, fiber-optic transmission lines or other optical media are being used instead of conventional metallic transmission lines to communicate signals in electronic systems due to the generally higher noise immunity and lower signal attenuation properties obtainable in such lines. Additionally, fiber-optic transmission lines are generally thinner and lighter than metallic conductors of comparable capacity.
In systems employing fiber optic transmission lines or the like, difficulties may arise due to degradation of the line resulting from physical damage, aging, poorly matched and/or damaged connectors, or for other reasons. In practice, difficulties with transmission lines are frequently difficult to detect and diagnose, particularly in electronic systems where only a single terminal end of the transmission line may be accessible. Although a number of different methods are available to detect and diagnose transmission line difficulties, one useful and commonly employed method is time domain reflectometry. In time domain reflectometry, an optical pulse or pulses may be transmitted into a fiber optic transmission line or medium. Any anomalies or defects may result in a reflected signal which may be detected by a time domain reflectometer. Such reflectometers are usually formed from standard components as opposed to custom parts to keep costs reasonable. These standard components, such as mixers or the like, may require appropriate input or drive signals and modulation signals for optimum operation and ability to effectively measure and analyze input pulses and reflected waveforms and mixed or modulated waveforms to detect any reflections at selected segments along a fiber optic transmission line or other optical medium.